1. Field of the Invention
This invention relates to a functional alloy which develops such effects as a shape memory effect, a superelasticity, and a damping effect.
2. Description of the Prior Art
Among well-known functional alloys which develop a shape memory effect, a superelasticity or a damping effect are Au-Cd, Cu-Zn-Al, Cu-Al-Ni, and Ti-Ni type alloys. Some of these functional alloys have been put to practical use but the upper limits of temperatures at which they can develop a shape memory effect are at most 100.degree. C. Thus, so far as the above alloys are used, it has been impossible to produce an alloy which restores its shape at high temperatures above several hundred degrees. Sometimes, to increase the transformation temperatures, various elements are added to these alloys, but heretofore a remarkable result has not been obtained.
Among various functional alloys, TiNi type alloys are superior in corrosion resistance. However, TiNi alloys have a drawback that their plastic workability is poor. Further, at present when a sufficient investigation of the carcinogenic effect of Ni ions on human tissue has not yet been made, there is a problem in the embedding of NiTi alloys as they are, in human bodies. Thus, when TiNi alloys are used as an implanting material for orthopedics, they must be coated.
On the other hand, as described in a variety of publications, such as the "Journal of the Less-Common Materials", 20 (1970) 83-91, Table II, FIGS. 4 and 5 and "Japan Institute of Metals Autumn Meeting Preparatory Manuscript" (1985, 10), it is known that near-equiatomic TiPd alloys have a martensitic transformation start temperature (hereinafter referred to simply as the Ms point) of 510.degree. C. and that they have a shape memory effect. Thus, if said TiPd alloys are used, it is possible to produce an element which restores its shape at high temperatures in the vicinity of 500.degree. C. However, no functional alloy which develops a shape memory effect at suitable temperatures between 100.degree. C. and 510.degree. C. has been put to practical use.